1. Field of the Invention
The present invention relates to a light-emitting polymer and an organic electroluminescent display using the same, and more particularly, to a blue light-emitting polymer and an organic electroluminescent display of which brightness and efficiency property are improved using the polymer.
2. Description of the Related Art
An organic electroluminescent display is largely classified according to an organic film-forming material and a manufacturing process into a display using a small molecule and a display using a polymer material. When preparing the display using a small molecule, a thin film is formed through vacuum deposition. Accordingly, a light emitting material can be highly purified, and a color pixel can be easily embodied. However, improving quantum efficiency, preventing a thin film from crystallizing, and improving color purity are still to be solved.
Research concerning the electroluminescent display using a polymer material is actively being conducted since it was reported that poly(1,4-phenylenevinylene) (PPV), a π-conjugated polymer, emits light when a current is applied to it. The π-conjugated polymer has a chemical structure in which a single bond (or a σ bond) and a double bond (or a π bond) are present alternately, and π it electron is delocalized and can be moved freely following bond chains. Due to such semiconductor-like property, the π-conjugated polymer that emits the whole range of visible light corresponding to the highest occupied molecular orbital—the unoccupied molecular orbital (HOMO-UMO) band-gap when using it in a light-emitting layer of an electroluminescent display can be easily obtained by designing molecules. The π-conjugated polymer can form simply a thin film by spin-coating or a printing method, and thus a display preparation process using polymer material is simple and economical. The π-conjugated polymer also has high glass transition temperature, and thus, it can provide a thin film having superior mechanical property.
However, the organic electroluminescent display using a polymer material has problems such as low color purity, high driving voltage, low efficiency, etc., and thus research to solve such problems is in progress. For example, a poly(9,9-alkylfluorene) (PAF) or a fluorine-containing copolymer (see U.S. Pat. No. 6,169,163 entitled Fluorene-containing Polymers and Compounds Useful in the Preparation thereof to Woo, et al., and issued on Jan. 2, 2001.) exhibits high light-emitting efficiency and high efficiency in color images through copolymerization, but the lifetime of the material itself is short due to photooxidation and a defect within the backbone of the polymer. Thus, the short lifetime of a light-emitting polymer, particularly the blue light-emitting polymer, has hindered the development of the organic electroluminescent display.
Research results that a spirofluorene compound can be used as a blue light-emitting polymer are reported in U.S. Pat. No. 5,621,131 entitled Conjugated Polymers having Spiro Centers and their Use as Electroluminescence Materials to Kreudo, et al. and issued on Apr. 15, 1997 and U.S. Pat. No. 5,763,636 entitled Polymers containing Spiro Atoms and Methods of Using the Same as Electroluminescence Materials to Kreudo, et al. and issued on Jun. 9, 1998, and Japanese Patent Publication No. 2002/326965 entitled Spirofluorene Compound, Method for Producing the Same, Intermediate for Synthesizing the Same, and Organic Electroluminescent Element Using the Spirofluorene Compound to Tetsuaki, et al. and published on Nov. 15, 2002.